The development of neuromuscular junctions will be studied in vitro where the process can be dissected by the methods of biochemistry, electrophysiology and electron microscopy. Clonal cell lines of nerve and muscle and primary cultures derived from Xenopus embryos will be used in these studies. The mechanism of acetylcholine receptor localization and other trophic effects of innervation will be investigated. Synaptogenesis will be studied in vivo during development of diaphragm muscle. The defect in myasthenia gravis will be investigated. The mechanism by which antibody against the acetylcholine receptor increases receptor degradation will be studied.